Filters, particularly low pass filters, are used extensively in electrical circuits to suppress noise. For high impedance, high frequency circuits pi-network filters are generally used. The pi-network is comprised of a shunt capacitor at both ends and a series inductor between.
The elimination of high frequency noise is necessary for the transmission of signals through the input/output devices of microcomputers, for example. Both individual pi-network filters and composite pi-network filter assemblies have been used in connectors. Generally, the assemblies such as those disclosed in U.S. Pat. Nos. 4,262,268 and 4,494,092 have capacitor assemblies comprising a pair of dielectric plates having a plurality of openings formed therein for receiving individual terminals. The dielectric plates have a plurality of isolated electrodes formed on one of the opposite faces of the plates adjacent respective openings formed therein for receiving individual terminals and a common electrode formed on the other face of the dielectric plates to provide for ground return. The terminal members extend through one dielectric plate, a tubular or planar magnetic member interposed between the first dielectric plate and a second dielectric plate. The terminals are mechanically and electrically connected to the respective electrodes on each dielectric plate. The assembly also includes means for electrically connecting the common electrodes to an external circuit. Generally the means requires soldering or otherwise electrically connecting the respective common electrodes on the two dielectric plates to a grounding means in the shell of the housing in a two step operation. Generally the soldering of at least one of the electrodes on the dielectric plates is "a blind operation", that is the solder is put in place within the shell member before the component, the component thereby blocking view of the soldered connection.
U.S. Pat. Nos. 3,579,155 and 3,597,711 disclose filter sleeve construction for individual terminals. The filter member of the '155 patent is comprised of a plurality of innersleeve magnetic ferrite members surrounded by an outer ceramic sleeve member. The '711 patent discloses a filter assembly having a single inner core of a magnetic ferrite material and an outer core of a dielectric material. The filter members disclosed in the above two patents have a pi-network configuration. The diameter of the filter members and therefore the diameter of the sleeve members is limited by the design of the connector in which the filter member is used and in particular to the configuration on the mating faces of the connector. Since one sleeve or one layer is completely encased within another, the thickness of respective layers is relatively thin. Thin walled sleeve members are generally more fragile and more costly to manufacture than members having thicker walls. In addition, the concentric sleeve arrangement requires greater restriction of tolerances since for any given filter, there are at least two inner and two outer dimensions that must be controlled.
It is desirable, therefore, to provide a filter assembly having component members with thicker walls, while maintaining the center line mating configuration of the terminals to which the filters are mounted.
Additionally it is desirable to have a filter assembly that can be made in an automated manufacturing process and in a cost effective manner.
It is also desirable to have a means for providing a pi-network filter assembly for an electrical connector that can be electrically connected to ground means within a shell without the need for "a blind soldering operation".